This invention relates to an apparatus and method for decoding and providing coherence for less expensive, incoherent fiber optic bundles. The apparatus and method provides a robust and inexpensive method and apparatus for transmitting visual or infrared coherent images.
There are two types of fiber optic bundles: coherent and incoherent. Coherent fiber optic bundles are used to provide spatially intact representations of images. Because each fiber must have the same spatial position at the input and output faces, their manufacturing costs are much higher and thus more expensive. Incoherent fiber bundles, also called light guides, can be made in very long lengths because the fibers do not have to be spatially oriented in any specific manner.
A coherent imaging bundle must be manufactured very carefully in order to maintain the spatial orientation of the fibers at the input and output of the bundle. This is typically a build-up process involving gluing a single fiber layer together in a flat tape then building up layers of these tapes. The fiber placement at the ends is fixed by gluing and crimping a binding fitting. The ends are then ground and polished flat. This is a high cost process with inherent limitations on the size of bundles that are feasible and the temperature ranges which are limited by the glues.
The basic concept for imaging with incoherent fiber bundles requires that the spatial relation between each fiber input and output is precisely mapped for digital processing. The image formed on the input face of an incoherent bundle is a xe2x80x9cscrambledxe2x80x9d incoherent image at the output. The incoherent image is xe2x80x9cunscrambledxe2x80x9d by digitally remapping the output pixels to the correct location. Once a bundle has been mapped, the map becomes a property of the bundle which allows all input images to be resolved.
Thus, it should be apparent that due to lower costs and easier manufacturing it is advantageous to utilize incoherent fiber bundles for coherent image transmission.
U.K. patents 2,082,012; 2,092,859; and 2,128,883 and U.S. Pat. Nos. 5,327,514 and 5,515,470 are directed to methods and apparatus for calibrating fiber bundles for image transmission using a series of image patterns. U.S. Pat. Nos. 5,327,514 and 5,515,470 are specifically directed to coherent image transmission through incoherent fiber optic bundles. U.S. Pat. No. 5,327,514 discloses a method for calibrating an incoherent fiber bundle for image transmission using a series of image patterns. U.S. Pat. No. 5,515,470 discloses a method for reconstructing a coherent image given a set of known input and output fiber coordinates.
Although these prior inventions succeed in calibrating the fiber bundle and reconstructing the incoherent images, they do not address the sensitive nature of the bundle-specific calibration matrix which becomes void and unusable once any part of the fiber bundle to video camera interface is disturbed. For example, these prior inventions do not account for transmitting infrared images, because infrared wavelength images require different focusing than visible wavelength images. The incoherent-to-coherent calibration of the prior art does not allow refocusing of the optical interface since that would modify the coordinates of a fiber bundle""s output fibers. Thus, the present invention provides not only a simpler approach to calibrating an incoherent fiber bundle but also a robust method for the end-user to switch video cameras, use alternative bundle-to-camera optical interfaces, or refocus the existing interfaces such as to transmit infrared wavelength images.
An object of the present invention is to provide apparatus and methods for decoding and providing coherence for incoherent fiber optic bundles.
It is another object of the present invention to provide apparatus and methods to produce a robust and inexpensive means for transmitting visual or infrared coherent images.
Still another object of the present invention is to provide a two-part means for using incoherent fiber optic bundles for visual or infrared image transmission where the calibration may be transformed to use different cameras or optical interfaces.
Yet another object of the present invention is to provide a two-part method of calibrating incoherent fiber optic bundles to transmit visual or infrared coherent images which consist of the following: 1) provide a fast and simple method for obtaining the coordinates of the fibers on the input and output face and how they relate to each other based on an initial camera and optical interface and 2) provide a method to allow the output fiber coordinates to be transformed for alternative cameras, optical interfaces, or the refocusing that is required when transmitting infrared images. Part 1 would be performed by the fiber bundle supplier using a simple hardware apparatus and software algorithms defined herein. Part 2 would be performed by the end-user using software algorithms along with the initial fiber coordinates and images as explained herein.
Part 1 to define the initial coordinates of the input and output fibers is achieved by an apparatus having the following characteristic features. A computer monitor is mounted on a lab bench with the screen orthogonal to the input face of the fiber optic bundle and attached objective lens. The output face of the fiber optic bundle is coupled with a charge-coupled device (CCD) video camera with a focusing lens between them. The video camera-signal is digitized into still images using a video frame grabber board.
Part 2 to transform the coordinates of the fibers on the output face of the bundle for different configurations is achieved by an apparatus similar to that in Part 1 except the video monitor and the input face of the fiber optic bundle no longer face each other.